1. Field of the Invention
The present invention relates generally to a self-testing control system for an internal combustion engine, and more particularly to a control system, preprogrammed memory unit having a program for testing the microcomputer so it executes necessary decisions and processes.
2. Description of the Prior Art
Recently, various control systems using a microcomputer have been developed to control operating values of an internal combustion engine; typical controlled operating values are fuel injection rate, ignition timing, exhaust gas recirculation, catalyst temperature, etc. A conventional analog or digital circuit for controlling an internal combustion engine operating value, is usually be tested by supplying a particular input signal to an actuator that affects the operating value. An output value obtained in response to the actuator being driven by the input signal is compared with a predetermined reference value. In this case, since a conventional circuit is relatively simple in structure, it is comparatively easy to test the circuit. On the other hand, in a control system using a microcomputer having a central processing unit (CPU), it is not possible readily to extract the necessary data from the CPU and to decide whether the control system is operating normally since all the arithmetic operations are executed in the CPU in time sharing mode. Even if such testing were possible, it would be complicated and expensive to realize a test program for testing such a control system using a microcomputer.
In addition, it is very difficult to decide whether the microcomputer is out of order, or whether the actuators and sensors for controlling the above-mentioned operating values, such as fuel injection rate, ignition timing, and exhaust gas recirculation, are not operating, or whether other electrical circuits, than the microcomputer, or mechanical parts are damaged. Therefore, when repairing the system in a repair shop it is necessary to test the system by removing the microcomputer completely even if the microcomputer is in fact operating normally.
In addition, the microcomputer is generally installed in the control system at a position where it is relatively difficult to remove, from the standpoint of protection from vibration; accordingly it is more difficult to conduct a test of the microcomputer provided for a control system with the microcomputer installed in position.